Method for recovering and separating metals from waste streams

ABSTRACT

A method for recovering and separating precious and non-precious metals from waste streams, which removes, separates, and recovers such metals in a cost effective manner with more than 95% removal from waste streams and with minimal amounts of unprocessed solids and sludge remaining in the environment. Metals such as chromium, manganese, cobalt, nickel, copper, zinc, silver, gold, platinum, vanadium, sodium, potassium, beryllium, magnesium, calcium, barium, lead, aluminum, tin; and the like are removed and recovered from the waste streams with at least 95% removal and other metals and compounds, such as antimony, sulfur, and selenium are removed and recovered from waste streams with at least 50% removal. The method employs a unique complexing agent comprising a carbamate compound and an alkali metal hydroxide which facilitates the formation of the metals into ionic metal particles enabling them to be readily separated, removed and recovered.

This is a cont. of Ser. No. 08/696,321 filed Aug. 13, 1996 now U.S. Pat.No. 5,753,125 which is a cip of Ser. No. 08/445,353 filed May, 19, 1995,now abandoned.

FIELD OF THE INVENTION

The present invention relates generally to a method for removingprecious and non-precious metals from hazardous and non-hazardous wastestreams, and more particularly to a method for recovering and separatingsuch metals.

BACKGROUND OF THE INVENTION

Treatment and reduction of concentrations of metals in metal bearingindustrial waste streams to environmentally acceptable levels has been along term problem. It is important to be able to treat such wastes andremove metals, hazardous materials, and toxic substances, with minimalamounts of solid wastes remaining in a cost effective manner. Theultimate solution to such environmental problems, recovery, recycling,and reuse of metals contained within waste streams has been inadequatelyaddressed.

In those instances where metals, compounds, and hazardous materials arenot separated from waste streams, but are transported to special wastedisposal facilities for treatment or storage, the metals are notrecovered, leaving them to be disposed of with other unprocessed orpartially processed wastes. As a result, not only is there no recyclingwith the attendant potential for economic profit or cost reduction, butwaste disposal and waste storage problems are created as well. Suchwaste disposal and waste storage problems are associated with high costand long waste storage time periods. Often, the wastes generated areconsidered to be hazardous. Under many environmental statutes,hazardous, toxic, and/or dangerous wastes remain the liability of thewaste generator, as long as these wastes exist in the environment. Suchlong term liability remains with the generator, even though the wastesmay have been treated and placed in a secure landfill for disposal.

Processes for removing metals from waste streams including ion exchangeand electrolysis have heretofore been known, but theses process arelimited. Ion exchange is costly, slow, and cumbersome to use, and inorder to be effective, the waste water being treated must be passedthrough a significant amount of ion-exchange resin, usually in the formof a filter bed, making it effective, in most cases, for only treatingsmall volumes of waste water. The complex fabrication process andsophisticated synthetic chemistry required by ion exchange metalrecovery technology significantly contributes to the expense of its useto purify liquid waste streams. The cost and complexity of ion exchangealso limits the variety of resins available.

Although ion exchange resin beds may be regenerated, the waste watersfrom regeneration must often be retreated to remove bulk contaminantsand then usually passed through the ion exchange resin again toeliminate hazardous materials. Thus, ion exchange is a cumbersomeprocess, and therefore impractical, especially for large volumes ofwaste water in a continuous-treatment process, as compared to usingion-exchange in a batch-treatment process.

Electrolysis is also expensive, requires significant maintenance,employs other resources, may create its own waste disposal problems andis energy intensive. Electrolytic recovery is, at best, 70%-80%efficient. Besides, the electrolyte systems available today are verysensitive to the presence of contaminants.

Use of either ion exchange or electrolytic recovery of metals from wastestreams requires separation of streams for processing, therebyultimately creating multiple waste streams. This multiplicity of streamsresults in a costly waste removal process for the waste streamgenerator.

In contrast to the ion exchange and electrolytic metal recoveryprocesses, one of the more acceptable technologies for treating wastewater is based on a settling process, using fixating agents such ashydroxides and sulfates. The fixating chemicals are added to water in asettling tank to absorb or otherwise transform the contaminants intomaterials which settle to the bottom of the tank. This technology usescomparatively simple equipment and permits the processing of largevolumes of waste waters, without adding materials which would result inan environmentally undesirable effluent stream. However, in many cases,use of ordinary settling processes fails to reduce contaminantconcentrations to levels low enough to meet the statutory requirements,without using excessive amounts of materials, over a protractedprocessing time. Current settling processes often produce undesirablylarge quantities of solid hazardous or toxic wastes in the form ofsludge. The sludge cannot, for the most part, be effectivelyregenerated. Thus, using current settling techniques for waste watertreatment, the resulting sludge product is yet another waste materialthat must be disposed of in a secure landfill without benefit ofrecycling. In turn, this process results ultimately in the necessity toclean the environment in the long term future.

As a result of problems associated with the above noted technologies,waste water generators have been forced to consider alternative methodswhich employ the addition of metal complexing agents to waste waterstreams and sludge of various industrial processes.

For example, U.S. Pat. No. 3,966,601 (Stevenson, et al.) discloses apurification process comprised of mixing a soluble heavy metal salt anda heavy metal dithiocarbamate. U.S. Pat. No. 4,387,034 (Unger, et al.)discloses a collector for use in concentrating metal values in ores byflotation, the collector being comprised of a mixture of 0-isopropylN-ethylthionocarbamate and o-isobutyl N-methylthionocarbamate.

U.S. Pat. No. 4,578,195 (Moore, et al.) discloses a process for treatingaqueous effluents to remove polluting metallic elements wherein theeffluent is contacted with a poly(dithiocarbamate) chelating agent. U.S.Pat. No. 4,612,125 (Elfline) discloses a method for removing heavymetals from waste water streams, comprising treating the waste waterwith sulfur-containing compounds, such as sodium tri-thiocarbamate.

U.S. Pat. No. 4,678,584 (Elfline) discloses a method for treating aliquid containing a heavy metal comprising contacting the liquid with amixture of sodium diethyldithiocarbamate and sodium tri-thiocarbanate.U.S. Pat. No. 4,943,377 (Legare) discloses a method for removing heavymetals from waste effluents comprising mixing the effluents with asolution of a sulfur compound such as sodium polythiocarbamate. U.S.Pat. No. 5,372,726 (Straten) discloses a method for treating waterpolluted by metal ions comprising the steps of adding thiocarbamide,potassium or sodium hydroxide, and potassium or sodium hyposulfite.

U.S. Pat. No. 5,264,135 (Mohn) discloses a method for treating sludgefrom industrial waste water streams comprising the steps of adding ametal complexing agent to the sludge such as dimethyl-dithiocarbamate ora salt thereof. The metal complexing agent is added to a sludgethickening tank prior to de-watering in a filter press to form a sludgethat contains 60% to 85% moisture by weight. Mohn does not disclose usesource separation of the effluent throughout the process and does notdisclose adjusting the pH of the waste solution to the optimal point ofinsolubility for the various metals involved. Mohn characterizes thesludge as being fixated, thereby allowing disposal in landfills.

In addition, a number of metallurgical processes for recovering metalhave also been disclosed. For example, U.S. Pat. No. 3,899,322 (Yosim etal.) discloses a process for recovery of noble metals from scrapcomprising melting the scrap at a temperature between 800° F. and 1,800°F. U.S. Pat. No. 4,135,923 (Day) discloses a process for the extractionof metals from metallic materials comprising heating a lead-free mixtureof metals and separating the metals in a molten state.

U.S. Pat. No. 5,008,017 (Kiehl, et al.) discloses a process forrecovering metals from waste liquids, including a step for obtainingpure metal. A dewatered sludge is heated for a period from about thirtyminutes to about one hour at 900° F., to recover substantially puresilver. However, this metallurgical process for recovering metals from ametallic sludge is very complicated, and requires a metal complexingagent be applied to the metallic sludge of waste streams.

None of the known prior art technologies separate and also recover avariety of metals from one or more waste streams in order to use themetals as valuable commercial products, nor do they disclose therecovery, recycling, and reuse of the recovered metals. In those priorart processes using reagents to cause fixation of metals and to producea fixated hydroxide sludge byproduct, the resulting byproducts must besent to and disposed of in a secure landfill or alternative receivingsite.

For the foregoing reasons, there is a need for a method for removing,separating, and recovering metals and groups of metals, such astransition metals, alkali metals, and alkaline earth metals. Anefficient method for removing, separating, and recovering such metals ina cost effective manner with a high degree of recovery from wastestreams and with minimal amounts of unprocessed solids and sludgeremaining in the environment is needed. Illustrative, but notlimitative, of the metals that such a method can be capable ofseparating, removing and recovering are such precious and non-preciousmetals as aluminum, barium, beryllium, calcium, chromium, cobalt,copper, gold, iron, lead, magnesium, manganese, nickel, platinum,silver, tin, vanadium, zinc, and the like.

Such a process should also be capable of removing other metals such asantimony, arsenic, selenium, thallium, and the like from waste streamswith at least 50% removal.

SUMMARY OF THE INVENTION

The present invention is directed to a method for recovering andseparating precious and non-precious metals from hazardous andnon-hazardous industrial waste streams. The method of the presentinvention removes, separates, and recovers such metals in a costeffective manner with more than 95% removal from waste streams and withminimal amounts of unprocessed solids and sludge remaining in theenvironment.

The method of the present invention for separating and recoveringprecious and non-precious metals from industrial waste stream generallycomprises: adjusting the pH of an industrial waste stream containing theprecious and non-precious metals to be recovered; adding a metalcomplexing agent to said waste stream to form metal ions of the metalsto be recovered; adding a particle growth enhancer to promote theaggregation of said metal ions; adding a flocculating agent to increasethe particle size of said metal ions and form a solution thereof;dewatering said solution to form a sludge and a supernatant; dewateringand drying said sludge to form an ionic metal concentrate; and, meltingsaid concentrate to selectively remove and recover a desired metaltherefrom.

DETAILED DESCRIPTION OF THE INVENTION

In accordance with the present invention, a method for recovering andseparating metals from waste streams, comprises the following steps:

pH of a waste stream is adjusted;

a metal complexing agent is added;

a particle growth enhancer is added;

a flocculating agent is added resulting in a solution;

the solution effluent is then dewatered, preferably using a plate andframe press, resulting in a sludge and a supernatant; and

metals are recovered from the sludge upon melting, drying and dewateringa filter cake with melting enhancers so as to permit selective removalof a fused metal-bearing concentrate for casting into ingots to be soldto primary smelters.

A suitable base such as sodium hydroxide (NaOH) or calcium hydroxide(Ca(OH)2) or a suitable acid such as hydrochloric acid (HCL) can be usedto adjust the pH of the waste stream from about 5 to about 13,preferably from about 7 to about 12, depending upon the initial pH ofthe waste stream to be treated and the metal(s) desired to be recovered.

The metal complexing agent that can be used comprises a mixture of acarbamate compound, an inorganic base, and water. The carbamate that canbe employed are those selected from the group consisting ofthiocarbamates, dithiocarbamates, alkylthiocarbamates such asdimethyldithiocarbamate and diethyldithiocarbamate, and salts thereof.The inorganic bases that can be used are those selected from the groupconsisting of sodium hydroxide, calcium hydroxide, potassium hydroxide,and the like. A preferred complexing agent comprises a mixtureconsisting of about 40% by weight sodium dimethyldithiocarbamate; about10% by weight sodium hydroxide; and, about 50% by weight water.

The particle growth enhancer is employed to promote an ionic exchangewith the metals in solution and to provide a foundation upon which theionic metal particles can grow. The preferred particle growth enhancerused is an aqueous solution of calcium chloride comprising about fiftypounds (50 lbs.) calcium chloride dissolved in about 100 gallons (gals.)of water in combination with an ionic exchange promoter. The ionicexchange promoter employed is ferric chloride (FeCl3) which iscommercially obtained as a 38% liquid solution. The amount of ionicexchange promoter used can range from about 0.03% to about 0.4% byvolume.

The flocculating agents employed in the method of the present inventionare commercially obtained material typically available as solid,granular ionic polymers having a medium anionic charge. Theseflocculating agents, together with the particle growth enhancer and theionic exchange promoter, cause the ionic metals in solution to increasein size and weight, precipitate, and settle. Illustrative flocculatingagents that can be used include Clarifloc A-3020 available from PolyPure, Inc., Parsippany, N.J.; Floculite 402 available from Dubois,Cincinnati, Ohio, and J. Flock 711 available from Jamestown Chemical,Westhaven, Conn. The flocculating agent is prepared as a diluted aqueoussolution consisting of one pound of the flocculating agent in 65 gallonsof water and then further diluting this concentrate in 200 gallons ofwater. This dilute solution is then used in concentrations of from about0.001% to about 0.01% by volume. The preferred flocculating agentemployed is Clarifloc A-3020.

When the industrial waste stream to be treated contains organiccompounds, they are initially degraded or destroyed by using a suitableoxidizing agent such as sodium hypochlorite, hydrogen peroxide at 35% to50% concentration, ultra violet (UV) radiation or ozone (O3). When anoxidizing agent is used, the waste stream should be monitored to assurethat an oxygen reduction potential (ORP) of about +350 my is achievedand maintained for a period of about 15 minutes before treating thewaste stream with the method of the invention.

Similarly, when the industrial waste stream to be treated is found tocontain chelating agents (e.g., hexavalent chromium) these agents areinitially or destroyed by using a suitable reducing agent such as sodiummetabisulfite, sodium sulfide, and the like. The waste stream should bemonitored until the presence of the undesirable chelating agent can nolonger be detected.

The method of the invention includes the following steps:

a. Waste streams to be treated are analyzed to determine the types ofwastes and metals present, whether the waste streams contains preciousmetals or non-precious metals; volatile organic compounds (VOCs); solidsabove 5% by volume, chromium above an average of 15 parts per million(ppm); and cyanide.

All incoming wastes are classified by priority metal which in a givenwaste solution to be treated, is the metal found most prominently. Themost prominent metal is analytically identified. For example, a wastesolution containing 1000 ppm of copper and 200 ppm of cadmium has copperas the priority metal and cadmium as the secondary metal.

b. Incoming waste streams are separated according to the priority metal,identified by the analytical procedures for each respective wastestream. Waste solutions with common dominant metals are mixed togetherfor processing. For example, a solution containing 1000 ppm or more ofcopper is mixed only with a waste solution containing a priority metalof copper, since to do otherwise would reduce the concentration ofcopper in the final metal recovery product. Recovery product is sold toprimary smelters based on the level of the priority metal. As thepriority metal is removed, the secondary metals are all concentrated andthe process moves to the next level based on the new priority metalselected from the remaining waste solution. Thus, a continuing recyclingprocess takes place removing each priority metal successively.

c. The pH of the waste streams is adjusted, as required, to increaseinsolubility of the priority metal with ionically bonded compounds andto precipitate ionic metal particles upon addition of a reagent. Theoptimum pH level will vary from 7 to 12 depending on the priority metalbeing addressed in the waste solution. For purposes of selectiveseparation, the priority metal is the most prominent metal determined byanalysis, i.e., the metal which the aforementioned analysis reveals tobe present in the highest concentration.

d. The reagent, in the form of a metal complexing agent is added tochelate certain metals from ionically bonded compounds. These metalswill ultimately be removed and recovered from the waste water. The metalcomplexing agent comprising a dithiocarbamate and preferably comprisingabout 40% sodium dimethyl dithiocarbamate, about 10% sodium hydroxide(NaOH) and about 50% water is used.

e. In the continuous treatment process described herein, 30 gallons ofthe aqueous calcium chloride particle growth enhancer solution is firstadded to a primary reaction tank containing 1,400 gallons of waste wateras described herein below. When the contents of the tank are processed,CaCl₂ is added to the flash mix tank continuously.

f. When the ferric chloride ionic exchange promoter is used, it is addedto the primary reaction tank used during the continuous treatmentprocess and is also added directly to the tank in the batch treatmentprocess.

g. Sodium hydroxide (NaOH) or calcium hydroxide Ca(OH)₂ is added to themix, the choice of which to use depends on the solution's sensitivity topH change. A solution which is heavily buffered (resistant to pH ofchange) is first treated with Ca(OH)₂ and then fine-tuned with NaOH. Onthe other hand, a solution that has little or no buffering and is thussensitive to pH change, will be adjusted with NaOH only. The hydroxideis added to adjust pH to the optimum level for the priority metals, asdiscussed more fully below;

h. As described above, flocculating agents are added to the mix, asdescribed below, to cause the ionic metallic precipitant to increase insize and weight and settle.

As the diluted working solution is used, proportional amounts of theflocculant concentrate and water are added to replenish the working tankas make-up flocculating agent.

The flocculant polymer solution is added to the continuous treatmentprocess by injecting it into the flash mix tank on a continuous basis.The amount of flocculant polymer added is in proportion to the amount ofdissolved and suspended solids in the waste being treated. Theflocculant is preferably used in concentrations ranging from about0.0001% to about 0.01%.

i. Oxidation and reduction are used, as required. Waste solutionscontaining both hexavalent chromium and cyanide ions, such as certainplating solutions, requires oxidation first and reduction second toensure that metal separation is complete. Thus, there are casesrequiring both oxidation and reduction.

In those cases where oxidation and/or reduction is required prior toprocessing the wastes, the wastes are first processed in a batchoperation as described under "Batch Treatment" below.

j. Heavy particles settle, resulting in a sludge and the supernatant isclarified and discharged. The sludge is thickened and dewatered, andmetals are recovered from the resulting thickened and dewatered sludgeas described below.

k. The present invention recovers metals, in the form of a dried powder.The metal-recovery dried powder may be either melted as specified andpreferred in the present invention or, alternatively, the metal-recoverydried powder may be sold to the smelter, where the product is used as afeed stock in place of a virgin product in the smelting operation.

The final and preferred step in the metal recovery of the presentinvention occurs with the melting of the ionic metal compounds. A flux,preferably a mixture of sodium tetra borate pentahydrate and soda ash,is added to facilitate this melting step. Sodium tetra boratedecahydrate and sodium tetra borate anhydrous may be used in place ofsodium tetra borate pentahydrate. The ionic metal compounds are meltedand then allowed to cool, resulting in solid recovered metal products.

The resulting metals are recovered and separated by priority metal andare sold to secondary and primary smelting operations. The presentinvention provides the raw material feed stock for the smelting recoveryof the metals recovered as ionic compounds from waste streams. Forexample, a recovered product containing copper as the primary metal issold to a primary copper smelter.

Waste streams containing large amounts of metals such as concentrationsequal to or greater than 2000 ppm (0.02% dissolved solids) and specificsolutions such as photographic wastes are treated in batch. In the batchtreatment, all operations occur in the same treatment vessel, i.e., avolume of waste is placed in a tank, reagent is added, and the solutionis allowed to settle, leaving the clean supernatant at the top andprepared and/or ready for discharge.

In comparison to batch treatment, continuous treatment is used for wastesolutions and in those cases where the volume of the waste stream is inexcess of 2000 gallons. In continuous treatment the waste solution istreated in different tanks, each tank being used generally for adifferent purpose. The wastes are moved from one tank to anotherallowing sufficient residence time for the solution to be processed ineach tank and for the required chemical processes to take place.Solutions move at rates varying from about 5 gallons per minute gpm! toabout 5000 gpm depending on the level of dissolved solids being removedfrom the solution.

In continuous treatment, the wastes are moved from a primary treatmenttank to a flash mix tank, to a flocculation tank, then to a gravitysettler tank, then to a filtration system, and finally to discharge. Thesolids that settle in the gravity settler are continuously removed to asludge settling and tank prior to de-watering. Continuous treatmentoperation is used to move large volumes of waste containing low levelsof dissolved contaminants rapidly through treatment.

Both the continuous treatment and batch treatment operations producesludge. The amount of sludge produced is directly related to the amountof dissolved metal in the incoming waste. As an example, a solutioncontaining one pound of dissolved salts will produce approximately onepound of sludge. Moreover, an input containing 60,000 mg/liter of copperand 0.15 mg/liter of lead would be typically left with 0.8 mg/litercopper and 0.02 mg/liter lead, which means that 59,999.02 mg/litercopper and 0.13 mg/liter lead could be recovered by the process of thepresent invention. In such case, the recovery rate for copper is99.9987% and for lead 86.666%.

CONTINUOUS TREATMENT OPERATION

In continuous treatment, incoming wastes are analyzed and are placed ina tank depending on the level of metal in the waste stream, volume to behandled and the reagents needed to cause metal separation.

Details of the continuous treatment process are as follows:

a. The waste stream is analyzed.

b. All incoming waste streams are classified by priority metals.

c. A solution containing a priority metal of copper, for example, isadjusted to a pH of 6 plus or minus 1 with an acceptable pH variation ofplus or minus 1, i.e., a pH range of from about 5 to about 7. The pH isadjusted using NaOH, Ca(OH)₂ or HCL depending on the initial pH of thewaste stream.

d. Once the pH of the waste is adjusted to the desired level, the metalcomplexing agent of the present invention is added, The waste beingtreated is allowed to mix with the metal complexing agent for about tenminutes. As above described, the complexing agent preferably comprisesabout 40% sodium dimethyl-dithiocarbamate, about 10% sodium hydroxideand about 50% water.

e. After mixing the wastes being treated with the metal complexingagent, calcium chloride solution is added and allowed to mix with thewaste for another ten minutes. The amount of calcium chloride addeddepends on the level of dissolved metals in the solution being treated.

f. Ferric chloride can be added, as required.

g. Additional pH adjustment, using sodium hydroxide or calcium hydroxidemay be required. The solution is then fed to a flash mix tank at a rateof from about 5 gpm to about 50 gpm, depending on the amount ofdissolved and suspended solids where additional calcium chloride andflock are added.

Where the total suspended and dissolved solids are below 0.01% the flowrate could be 50 gpm. This flow rate decreases proportionally as thelevel of dissolved and suspended solids increases, to where aconcentration of 0.5% will require a flow rate of approximately 5 gpm.Flow rates are dependent on the level of dissolved and suspended solidsand the type of equipment being used.

h. The solution then travels to the flocculation tank where it isthoroughly mixed allowing particle size growth. The residence time inthe flocculation tank is dependent on the level of dissolved solids inthe waste solution being treated. The tanks used are sized to allow aminimum of 10 minutes residence time at a flow rate of 50 gpm. For theflocculating reagent to work properly, a minimum residence time of 10minutes is required in 1,400 gallons for proper mixing and reaction.

i. After the required residence time in the flocculation tank, the wasteis fed to a flash mix tank where additional calcium chloride is injectedinto the waste stream to act as a binder to which the precipitatedparticles bind and begin to form particles of increasing size.

j. The solution is then passed into a clarification chamber withsufficient surface area to allow the heavy particles to settle to thebottom of the clarification chamber. Clean or clarified solution isremoved from the top of the clarification chamber and passing thereafterinto a sand filter to remove any small particulate matter that escapedthe flocculation and settlement stages and then the effluent goes to adischarge monitoring tank for pH monitoring and discharge.

k. At this point, the solution is fed to the gravity settling tank wherethe supernatant is separated from the solids. The solids settle to thebottom and are removed to the sludge thickening tank prior todewatering. The supernatant flows to the filter and finally todischarge. Solid heavy material is removed from the bottom of thesettlement chamber periodically. The settlement chamber, or gravitysettler tank is one in which clarification of the solution occurs by aprocess of settlement. The resulting solid or sludge is placed in asludge thickening tank where it is further settled into a conical shapedbottom of a large holding tank. As solids accumulate at the bottom ofthis settlement tank, they are drawn off by a pump and moved into aplate and frame filter press for de-watering. During this operation,excess water is removed from the sludge. The excess water isrecirculated back into the treatment system for further use.

l. This process produces an ionic metallic sludge with high metalconcentrations without the use of large quantities of reagents such ashydroxides, sodium borohydrate that would be placed in landfill fordisposal.

De-watered sludge is removed from the filter press. This material cancontain between 25% and 50% moisture by weight. The dewatered sludge orfilter cake is placed in infra-red dryers where the moisture content isbrought down to less than 20% by weight. The dryers operate attemperatures of between about 350° F. to about 600° F. depending on themetal content and the desired level of moisture for the recoveredproduct.

The resulting volume of recovered metal powder is reduced over theprevious de-watering step by as much as 30% to 50% by volume. The dryingprocess drives off the moisture and other compounds that are notmetallic leaving the metals in the resulting dry materials heavilyconcentrated.

m. The recovered dried metal powder is now converted to metallic metalby melting the recovered metal powder in gas-fired or electricalinduction melting ovens. The melting process is conducted in two stagesand depending on the feed stock can produce recovered metal ingots offrom about 50 to about 90 percent purity.

After de-watering and drying, the recovered metal powder is either soldas a commodity or is further converted to metal ingots. To convert therecovered metal powder to metal, which may be in the form of ingots, thepowder is placed into the melting oven where additional reagents aremixed with the recovered metal powder. The reagents added are sodiumtetra borate pentahydrate and soda ash.

Sodium tetra borate pentahydrate is added to the powder to cause themetals to liquefy once they reach the melting point. Soda ash is used tocause the metal to separate from the flux. Flux is the combination ofthe soda ash and sodium tetra borate pentahydrate (borax) used duringthe melting process.

The powder is first mixed with sodium tetra borate pentahydrate andmelted to cause a reduction in volume and produce a homogenous mixtureof metal and borax. This mixture is poured, cooled and re-melted in asecond melting oven where soda ash is added to cause separation in themelted state. This material is poured and allowed to cool.

Once cooled, the recovered metal, which has settled to the bottom of themold is separated from the slag comprised of the flux layer that is ontop of the recovered metal. The slag is reused in the next melt.

For those melts that produce clean black slag, the black slag is sold asa cleaning compound. For those melts that produce a semi pure slag, theslag is sold along with the metal to a primary smelter purchasing therecovered metal.

The temperature in the melting oven is brought up to approximately 1800°F. and the materials are allowed to melt until it is verified that allthe material in the crucible is liquid. This usually takes from 2-4hours depending on the temperature of the oven when it is first charged.For example, a melt from a cold oven will take about 4 hours, whereas amelt from a hot oven will usually take about 2 hours. At this point, themolten materials are poured into a cast iron buggy or mold that has beenpre-heated and coated with carbon to prevent the molten material fromsticking to the buggy walls. The purpose of the preheating is to driveout any residual moisture and ensure that the surface is not cold whenpouring in the molten bath. If the mold were cold, it might break fromthe sudden heat change or it might cause the molten bath to spray moltenslag out of the mold.

The material is allowed to cool and solidify at which time the resultingsolid is removed from the buggy and separated in two different layers.The material is then placed into a second melting oven where thetemperature is brought up to approximately 1800° and two additionalreagents are added, to induce the material to separate into threelayers.

The lower layer consists of 60% to 90% of the recovered metal such ascopper or nickel. The second or middle layer consists of pig ironcontaining all of the remaining metals, and the top layer consists ofslag, i.e., the flux containing the two reagents that were added, one toeach melt. The resulting products from this operation are solid and arecommercially recycled thus completing the recycling of the components inthe wastes. These materials can then be sold as feed stock for primarysmelting operations.

The above noted procedures to produce recovered metal ingot arerepresentative of each time the sludge is removed from the filterprocess. The amount of sludge removed is directly related to the amountof dissolved salts in the waste at the beginning of the metal recoveryprocess. For example, a solution containing 1 pound of dissolved saltsproduces approximately 1 pound of sludge.

BATCH TREATMENT

Batch treatment takes place in one of a number of different tanks and isa process that may be completed in the starting tank. A cycle ofoperations is completed, and the effluent is removed for discharge,while the metal recovery products are either removed or utilized forfuture batch processes, and the cycle is repeated.

This batch recovery method is used for solutions containing preciousmetals above 250 mg/liter and for non-precious metal solutionscontaining concentrations of a priority metal above 0.2% (2,000mg/liter).

In the batch process, one cycle of operations is completed and theeffluent is removed for discharge to the sewer while the metal recoveryproducts are either removed or utilized for future batch process and thecycle is repeated.

Upon completion of analysis and selective separation of priority metalsby the aforementioned processes, wastes containing precious metals aretreated, as follows:

a. All wastes containing precious metal with low chromium content,generally less than 10 ppm of chromium, are placed in a separate tankdedicated to such wastes and are subjected to batch treatmentoperations.

b. Chromium present in wastes at levels greater than approximately 10ppm interferes with removal of other metals from solution. When thechromium concentration of waste to be treated is generally greater thanabout 10 ppm, the waste must be separated from other waste treatment.All wastes containing precious metals with high chromium content areplaced in a separate batch treatment tank to undergo batch treatment forhigh chromium and precious metals. The high chromium waste is thenseparately treated as elsewhere described herein.

EXAMPLES

The following illustrative examples are set forth to demonstrate theutility of the present invention of a number of different waste streams.

Example 1

Example 1 illustrates treatment of a solution containing cyanide andmetals in concentrations more than 500 mg/liter.

Large volumes are handled in an appropriate size tank. The waste istransferred to the treatment tank using an air activated diaphragm pump.The waste is then tested for pH and Oxygen Reduction Potential (ORP).

The solution is maintained at a pH above 10.5 with the addition ofcaustic while the cyanide is oxidized using oxidizing reagents tomaintain an alkaline state within the solution. When the solutionreaches and maintains the desired ORP for the desired length of time, asample is taken and analyzed for cyanide content. This method controlsthe generation of heat and prevents uncontrolled chemical reactions.When all the cyanide has been oxidized and the batch is low enough inmetal content, any remaining wastes are integrated into the regulartreatment for metal recovery.

If the metal level is above 1000 mg/liter, the batch will be completedin the same treatment tank. If the metal level is less than 1000mg/liter, the solution is fed into a continuous treatment operationcontaining the same priority metal.

All unused oxidizer is driven off from the solution by reducing the pHto a point where the oxidizer will be liberated as a gas. The liberatedgas is trapped by an air scrubbing system attached to the treatmenttanks and neutralized prior to being discharged to the atmosphere. Thisprevents the oxidizer from neutralizing the metal complexing agents thatwill be added to the solution during this operation.

The ionic metal will drop out of the solution and become particulatematter. To increase the rate of settlement, the pH of the solution willbe adjusted to an ideal point of insolubility for the priority metal anda bindery agent such as calcium chloride will be added.

The solution is allowed to mix for a predetermined time at which point apolymer is added to cause the particles to increase in size. At thispoint, mixing is terminated and the solution is allowed to settle. Theclean effluent or supernatant is removed for monitoring and discharge,while the ionic metal sludge that settled to the bottom of the tank isremoved and placed in the sludge thickening tank prior to de-watering,drying and melting. Table I illustrates details regarding quantities ofreagents added:

                  TABLE I    ______________________________________    Treatment Reagents for Example 1    Step     Operation     Reagent    Quantity    ______________________________________    1        100 gallons   H.sub.2 O  3:1    2        pH to 8       Ca(OH).sub.2                                       30 gr.    3        Complexing Agent                           NA.sub.2 S   1 gal.    4        Complexing Agent                           *          0.5 gal.    5        pH 9.5        CA(OH).sub.2                                        3 gr.    ______________________________________

Elemental analysis of Example 1 metals:

    ______________________________________                             Measurement Procedure    Element       Amount     (United States Government)    ______________________________________    Arsenic       <0.050     SW-846 6010 ICP    Aluminum      2362.000   SW-846 6010 ICP    Barium        68.690     SW-846 6010 ICP    Beryllium     <0.001     SW-846 6010 ICP    Cadmium       0.010      SW-846 6010 ICP    Hexavalent Chromium                  <0.001     SM17-418.1 UV    Copper        418.000    SW-846 6010 ICP    Iron          203.400    SW-846 6010 ICP    Lead          3.280      SW-846 6010 ICP    Manganese     1.030      SW-846 6010 ICP    Mercury       0.073      SW-846 7470 AA    Nickel        0.500      SW-846 6010 ICP    Phenol        <0.020     SW-846 9065 UV    Selenium      <0.050     SW-846 6010 ICP    Silver        9.480      SW-846 6010 ICP    Zinc          0.620      SW-846 6010 ICP    ______________________________________

The physical analysis of Example 1 is:

    ______________________________________                            Measurement Procedure    Physical Attributes                 Results    (United States Government)    ______________________________________    Color        Dark Brown    Cyanide      <0.02      SW-846 9010    Flash Point  >200° F.                            SW-846 1010    Odor         None    pH           -0.21      SW-846 9040    Percent Solids                 <1%        SM17 2540b & 2540D    Specific Gravity                 1.02    Total Petroleum                 NA         SM17 418.1    Hydrocarbons    Viscosity    Medium    Layers When Standing                 1    Percent Moisture                 NA    ______________________________________

Example 2

In this example, a metal waste stream containing hexavalent chromium istreated. The pH of the solution is reduced to less than 2.0. A reducingagent such as sodium meta-bisulfate is added and allowed to react withthe waste for approximate 20 minutes to ensure complete contact andreduction of the hexavalent chromium to trivalent chromium.

The pH of the solution is adjusted to 3.5 and a volume of the metalcomplexing agent will be added. The pH will rise with this addition andthe ionic metal will drop out of the solution and become particulatematter. To increase the rate of settlement, the pH of the solution willbe adjusted to the ideal point of insolubility for the priority metaland a bindery agent such as calcium chloride will be added.

The solution will be allowed to mix for a predetermined time at whichpoint a flocculating agent will be added to cause the particles toincrease in size. Mixing will be terminated, and the solution will beallowed to settle. The clean effluent or supernatant will be removed formonitoring and discharged to the sewer while the ionic metal sludge thatsettled to the bottom of the tank will be removed and placed in thesludge thickening tank prior to de-watering, drying and melting.

Table II below sets forth the details of the reagents used:

                  TABLE II    ______________________________________    Treatment Reagents for Example 2    Step Operation    Reagent    Quantity    ______________________________________    1    100 gallons  H.sub.2 O  10:1    2    Reduce       NAHSO.sub.3                                 25 lbs./100 gal. of wastes    3    pH 7.00      CaOH.sub.2 60 lbs/100 gal. of waste    4    Complexing Agent                      NA.sub.2 S 0.2 lbs./1000 gal. of waste    5    Complexing Agent                      *          0.2 gal./1000 gal. of waste    6    Coagulant 1  CaCl.sub.2 5 gal./100 gal. of waste    7    Coagulant 2  Flocculating                                 1/4 lbs. per 100 gal.                      Agent    ______________________________________     * 40% sodium dimethyldithiocarbamate, 10% sodium hydroxide and 50% water

Elemental analysis of Example 2 metals:

    ______________________________________                             Measurement Procedure    Element       Results    (United States Government)    ______________________________________    Arsenic       20.00      SW-846 6010 ICP    Aluminum      7232.00    SW-846 6010 ICP    Barium        <0.01      SW-846 6010 ICP    Beryllium     5.30       SW-846 6010 ICP    Cadmium       108.60     SW-846 6010 ICP    Chromium      32070.00    Hexavalent Chromium                  146.60     SM17-418.1 UV    Copper        146.60     SW-846 6010 ICP    Iron          685.70     SW-846 6010 ICP    Lead          <0.01      SW-846 6010 ICP    Manganese     22.3       SW-846 6010 ICP    Mercury                  SW-846 7470 AA    Nickel        340.90     SW-846 6010 ICP    Phenol                   SW-846 9065 UV    Selenium      <0.05      SW-846 6010 ICP    Silver        74.10      SW-846 6010 ICP    Zinc          393.30     SW-846 6010 ICP    ______________________________________

The physical analysis of Example 2 is:

    ______________________________________                            Measurement Procedure    Physical Attributes                 Results    (United States Government)    ______________________________________    Color        Dark Brown    Cyanide      <0.02      SW-846 9010    Flash Point  >200° F.                            SW-846 1010    Odor         None    pH           -0.21      SW-846 9040    Percent Solids                 <1%        SM17 2540b & 2540D    Specific Gravity                 1.02    Total Petroleum                 NA         SM17 418.1    Hydrocarbons    Viscosity    Medium    Layers When Standing                 1    Percent Moisture                 NA    ______________________________________

Example 3

This example describes the treatment process of a precious metal bearingsolution containing chromium.

The pH of the solution is reduced to less than 2.0 with the addition ofhydrochloric acid (HCl). A reducing agent such as sodium meta-bisulfateis added to reduce the chromium. The solution is then agitated forapproximately 20 minutes to ensure complete contact and reduction of thechromium.

The pH of the solution is then increased to greater than 10.5 with theaddition of caustic reagents and a quantity of sodium hypochlorite isadded to oxidize any remaining chelating reagents. The oxidizer is addedin small quantities to prevent over feeding.

The pH is allowed to stabilize for approximately 15 minutes and is thenadjusted to a pH of 7.5, as necessary. If the pH drifts, additional pHstabilization is implemented.

Metal complexing reagents are added to the solution in sufficientquantity to cause all of the dissolved metal to precipitate out of thesolution.

After the desired settlement time, the solution is checked for metalcontent. Upon completion of the settlement process, the clean effluentis removed for monitoring prior to discharge, and the ionic metal sludgeis removed to a conical-bottomed sludge thickening tank prior tode-watering and drying.

When the sludge is transferred from the treatment tank to theconical-bottomed sludge thickening tank, a portion of the liquid is alsotransferred, in order to facilitate the transfer. Allowing separation ofsludge from transfer liquid in the conical-bottomed thickening tank issimply called "sludge thickening" and the tank in which it isaccomplished is so named.

Example 4

This example relates to a precious metal bearing solution (such asphotographic processing waste) without chromium. Recovery of the metalsfrom this type of solution is conducted in a batch operation for controlover the recovered product, reuse of the recovered product as a seed forthe next operation, cost of the complexing agent, keeping the solutionfrom outside contaminants and complying with regulations that exemptprecious metal recovery.

All material is placed in a large common holding tank. In this case, thetank has a capacity of 7,000 gallons, is closed topped and vented to theatmosphere through a permitted air scrubber. Once a sufficient quantityof material is placed in the holding tank, samples are obtained from thetop and bottom of the tank. These samples are analyzed for metalcontent.

A bindery agent such as calcium chloride is mixed by dissolvingapproximately 50 pounds of it in 100 gallons of water and the resultingsolution is fed into the holding tank by pumping it in through thebottom of the tank so as to ensure mixing and adequate contact with thesolution in the holding tank.

Based on the metal content, i.e., the concentration of suspended anddissolved metals determined to be present in the solution by chemicalanalysis, the metal complexing agent is fed into the holding tank bybeing pumped in from the bottom to ensure adequate contact with thesolution in the tank. The amount of complexing and bindery agents addedto the batch is directly related to the level of metal in the batch. Forexample, a 7,000 gallon batch containing 3,000 mg/liter of dissolvedmetal requires approximately 12 gallons of metal complexing agent and100 gallons of bindery agent to bring the metal levels to below 2mg/liter of combined metals. The tank is agitated from the bottom withair from an air pump for approximately 30 minutes to ensure adequatemixing of the bindery agent, metal complexing agent and the solution inthe tank. The contents of the tank are then allowed to settle forapproximately three to six hours, after which time samples are obtainedfrom the top and bottom of the tank for chemical analysis.Alternatively, the metal complexing agent can be added to the tank byitself to cause the separation and in such a case, CaCl₂ is not used.

Based on the analytical results which, under normal operating conditionsshows that the solution is clean, the clean effluent is removed by useof an electric centrifugal pump for pH monitoring prior to discharge.Monitoring occurs in a discharge holding tank just prior to sewerdischarge.

The precipitated ionic metal sludge is allowed to remain at the bottomof the tank as a seed for the next batch to be processed in this tank.Under normal conditions, this seed remains for five to six cycles beforeit is removed and the cycle is started over.

When the ionic metal sludge generated in this batch operation is removedfrom the processing tank, the sludge is placed into fifty-five gallonholding drums for storage prior to being processed in a dedicated filterpress. Effluent from the filter press operation is returned to thededicated batch process tank and reused.

De-watered solids from this operation are placed directly into a siliconcarbide crucible in a melting oven, where the solids are blended with aflux, i.e., sodium borate tetra pentahydrate and soda ash. For each 40pounds of recovered product that is placed in the first oven for stageone of the melting process, approximately three pounds of sodium tetraborate pentahydrate are added. For each melt in stage two of the meltingprocess, approximately 9-12 pounds of soda ash are added.

The melting oven is brought up to approximately 1800° F. and monitored.Once it is determined that the batch is in a homogenous liquid state bystirring, the contents of the crucible are poured into a cast iron buggy(mold) that has been pre-heated and coated with a carbon water solutionto prevent sticking of the molten material. The mold is allowed to coolfor 18 hours and the contents are removed and separated into threecomponents.

Noble metal (usually 95% or higher concentration silver), pig iron andslag is recovered. Both the silver and pig iron are placed into a secondmelting oven where additional soda ash is added and the oven is broughtto approximately 1800° F. Once it is determined that the batch is moltenby stirring the bath, approximately one pound of black iron is added tothe molten bath and allowed to completely melt. The bath is then stirredto verify that the black iron has melted.

After stirring is completed, the molten bath is poured into a pre-heatedbuggy (mold) that has been coated with carbon black to prevent themolten material from sticking to the sides of the mold. The mold isallowed to cool for approximately 14 hours at which time the mold isemptied.

The recovered products are removed from the mold and separated intothree layers consisting of a noble metal such as silver with a purity offrom 97% to 99.9%, a layer of pig iron containing all of the impurities,i.e., aluminum, cadmium, chromium, cobalt, copper, iron, manganese,nickel and zinc), and a layer of black slag.

The black slag is recycled two to three times in the same operationbefore it is sold as a scrubbing compound. The pig iron and silver areboth sold for their metal content completely recycling all of thecomponents within the incoming waste that caused the material to beclassified as waste.

Table III below sets forth the percentage of recovery for those metalsanalyzed in the incoming waste of Example 4.

                  TABLE III    ______________________________________            INCOMING   SUPERNATANT   PERCENTAGE    ELEMENT WASTE      AFTER RECOVERY                                     OF RECOVERY    ______________________________________    Arsenic <0.050     <0.050        0.000%    Antimony            <0.050     <0.050        0.000%    Aluminum            248.400    1.773         99.287%    Barium  <0.001     <0.001        0.000%    Beryllium            <0.001     <0.001        0.000%    Calcium 385.500    265.300       31.258%    Cadmium 1.560      <0.002        99.872%    Chromium            0.230      <0.005        97.826%    Cobalt  1.160      <0.003        99.741%    Copper  167.900    <0.002        99.999%    Iron    762.700    <0.005        99.993%    Lead    <0.025     <0.025        60.000%    Magnesium            396.500    17.540        95.576%    Manganese            161.900    0.250         99.846%    Mercury <0.020     <0.020        0.000%    Nickel  1.310      <0.010        99.237%    Phenol  <0.020     <0.020        0.000%    Potassium            16.340     8.230         49.633%    Selenium            0.060      <0.050        16.667%    Silver  0.010      <0.003        70.000%    Sulfate 8596.000   3400.000      60.447%    Thallium            0.800      <0.020        82.500%    Vanadium            0.470      <0.020        95.745%    Zinc    570.000    <0.004        99.993%    ______________________________________

Although the present invention has been described in considerable detailand with reference to certain preferred embodiments thereof, othervariations are possible. Therefore, the spirit and scope of the appendedclaims should not be limited to the description of the preferredembodiments contained herein.

What is claimed is:
 1. A process for recovering precious andnon-precious metals from effluent waste materials comprising the stepsof:a) feeding effluent waste solutions containing dissolved metallicsalts to a tank; b) monitoring said effluent waste solutions for pH; c)adjusting the pH of said effluent waste solutions to from about 3.5 toabout 10.5; d) feeding an oxidizer to said tank in an amount sufficientto assure that an oxygen reduction potential of no less than about 350is maintained for a period of about 15 minutes; e) feeding a reducingagent to said tank to remove any chelating agents present in saideffluent solutions; f) feeding calcium chloride as a bindery agent tosaid tank; g) removing a supernatant from said effluent solutions toform an ionic metal sludge; h) de-watering said ionic metal sludge to asubstantially anhydrous state consisting essentially of ionic metalpowders; and, i) melting said ionic metal powders to form metals fromsaid metallic salts.
 2. The process of claim 1 wherein said pH isadjusted to from about 5 to about 9.